CHAPTER 14 Cellular Reproduction 1

Overview of the cell cycle DNA replication DNA Damage and repair Nuclear and Cell Division Regulation of the Cell cycle Growth Factors and Cell Proliferation WILL NOT BE Included in the exam 2

Introduction Cells reproduce by the process of cell division. Mitosis leads to cells that are genetically identical to their parent. Meiosis leads to production of cells with half of the genetic content of the parent. 3

14.1 The Cell Cycle (1) The cell cycle is the series of stages that a cell goes through. It consists of the M phase and the interphase. – The M phase includes the process of mitosis and cytokinesis. – Mitosis last about an hour or so. – Interphase constitutes the majority of the cell cycle and lasts longer than the M phase (~23 hrs); – it may extend for days, week, or longer. 4

An overview of the eukaryotic cell cycle 5

The Eukaryotic Cell Cycle Cell growth === Cell division=== Cell proliferation -Duplication of DNA -Replication of DNA -DNA synthesis ---Mitosis/ Cytokinesis ---Regulation of Cell cycle Cell cycle Mitosis ~0.5 hrs 1-Starts--condension the chromatin 2a-sister chromatids 2b-nuclear envelop disorganize 2c-mitotic spindle 3-cytokinesis G1 8 to 10 hrs S 6 to 8 hrs G2 4 to 6 hrs ~23.5 hrs Go: the cell is out the cell cycle Go Terminal differentiation -Protein synthesis ? 6

The Cell Cycle (3) Cell cycles in vivo – Three cell types are distinguished based on their capacity to grow and divide. Nerve cells have lost the ability to divide, but not all of them. Liver cells divides in function of stimulus Stem cells will divide frequently. – Stem cells have asymmetric cell division in which the daughter cells have different fates. 7

The Cell Cycle (4) Control of the Cell Cycle – Cell cycle is focused on initiation of DNA replication and initiation of mitosis. – The cytoplasm contains factors that regulate the state of the nucleus. The cytoplasm of a replicating cell contains factors that stimulate initiation of DNA synthesis. The cytoplasm of a cell undergoing mitosis contains factors that trigger chromosomal condensation. 8

The stages of mitosis in animal and plants cells 9

Microtubule Polarity in the Mitotic Spindle Polarity of MT 10

Microtubule Polarity in the Mitotic Spindle Chromosome alignment and separation Separated by microtubules, also requires additional proteins like Topoisomerase II, changes in adhesive proteins, (anaphase) and motor proteins (three different roles--mitotic motors-) 11

Mitotic Motors 1.Kinetochore microtubules Plus & minus ends Depolymerases binds MT and induces depolymerization (chromokinesin, C-terminal and bipolar kinesin) 2.Polar microtubules ATP hydrolysis is require for MT sliding (C-terminal and bipolar kinesin) 3.Astral microtubules MT associated (cytoplasmic dynein) with cell cortex at plasma membrane (actin microfilaments) Taxol: it blocks MT depolymerization 12

Cytokinesis and Cell Plate Formation in a Plant Cell Youtube====50-year cell division puzzle solved Vesicles from Golgi and ER 13

Typical eukaryotic cell cycle --- G1, S, G2, M ---Control / Regulation Systems: 1--Appropriate time and sequence of events 2--Each event must be completed 3--Respond to external conditions (nutrients and growth factors) Cell cycle control: Key Transition Points in the Cell Cycle Chromosome segregation 14

Cell Fusion Evidence for the Role of Cytoplasmic Chemical Signals in Cell Cycle Regulation Specific molecules present in the cytoplasm that induce the transformation from S to G1 (DNA replication genes=proteins) from M to G1 (cell cycle regulation genes=proteins) Gene: cdc2=cell division cycle --regulate the transition from G2 to M --cdc2: protein kinase Regulation by phosphorylation? 15

Experimental demonstration that cells contain factors that stimulate entry into mitosis 16

Cell Cycle Regulation Mitotic M-cyclins Mitotic M-cdks S cyclins G1 cyclins G1 cdks How is the cell cycle regulated? Cdc2 ( Cell Division Cycle ) =kinase Kinase Phosphatase Substrate (P1) Substrate (P2) (Cyclins) =substrate (Cyclin-dependent kinase) -CDK- Cdc=cdk 17

Evidence for the Existence of MPF Maturation promoting factor=MPF =mitotic cdk-cyclin complex ----control the G2 to M transition 18

Fluctuating Levels of Mitotic Cyclin and MPF During the Cell Cycle Maximal Enzymatic Activity during the G2-M transition Substrate: degradation or synthesis? Regulation: phosphorylation or de-phosphorylation? CDK Relative activity 19

Phosphorylation and Dephosphorylation in the Activation of a Cdk-Cyclin Complex Ser= variable Thr= 161 Tyr=15 MPF-i mitotic cdk-cyclin complex=MPF MPF-a 20

Fluctuating Levels of Mitotic Cyclin and MPF During the Cell Cycle Maximal Enzymatic Activity during the G2-M transition Substrate: degradation or synthesis? Regulation:? Relative activity CDK 21

The Mitotic Cdk Cycle 1-Phosphorylation of lamin in the nuclear lamina induces depolarization 2-Phosphorylation of condensin induces chromosome condensation 3-Phosphorylation of MT induces polymerization 4-Phosphorylation of Anaphase promoting degradation complex. -APC-(ubiquitin ligase) Cell Cycle Control-I 22

The Anaphase-Promoting Complex and the Spindle Checkpoint Mitotic CDK-cyclin Anaphase promoting complex (ubiquitin ligase) 23

The Anaphase-Promoting Complex and the Spindle Checkpoint Regulation of the anaphase promoting complex: Binding with cdc20 APC cdc20 24

APC cdh1 -degradate mitotic cyclins SCF controls G1/S through G2/M transitions Ubiquitin ligase-degradation. SCF complex p27 and p21 (cyclin-dependent-kinase inhibitors (CKIs) G1/S cyclin, Cyclin E 25

Role of the Rb ( Retinoblastoma) Protein in Cell Cycle Control Cell Cycle Control-II G1 cdk cyclin 26

Cell Cycle Regulation Mitotic M-cyclins Mitotic M-cdks S cyclins G1 cyclins G1 cdks How is the cell cycle regulated?, 6 /A 27

DNA Damage: p53-dependent and independent pathways ---DNA damage: ?? can not be repaired-- Cell Cycle Control-III ATM kinase=ataxia telangiectasia mutated/mutation ATM=Ionizing radiation 28

ATR= UV radiation ATR kinase: Inactivation of cyclin DNA Damage: p53-dependent and independent pathways 29

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1.Spindle checkpoint Kinetochore attachment Mad, Bub, Cdc20 2.DNA replication checkpoint Completion of DNA synthesis G2/M transition Phosphorylation of mitotic cyclin 3.DNA damage checkpoint Cell cycle halted at various stages p53 – guardian of the genome Checkpoints=Cell Cycle Control Timer Cdk Cyclins A. DNA integrity (DNA damage) B. Processes (complete) 31

General Model for Cell Cycle Regulation Regulation Nutrients Mitogens EGF PDGF APC complex Growth factors Extra-cellular signals APC / SCF complex 32

Growth Factor Signaling via the Ras Pathway -bacteria and yeastcell proliferation/division -mammalian cellscell proliferation/division Nutrients Glucose Growth factor = mitogens 33

Growth Factor Signaling via the Ras Pathway 34

Growth Factor Signaling via the Ras Pathway Raf=MAPkkk MEK=MAPkk ERK=MAPk Mitogenic Activated Protein Serine/Threonine PM or endosomes Tyrosine 35

The PI3K-Akt Signaling Pathway Insulin (I) and Insulin-like growth factor (IGF) 36

EGF/ PDGF TGF-  (+) (-) Cell Growth / Proliferation Mothers Against Decapentaplegic (MAD) Small Mothers Against paralysis ( SMA) Phosphorylation of Smad Activation of p27, p21 and p15 (Cdk inhibitors) MAPK 37

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